When things like this happen, it can haunt you for years, and if you don't work at it, understand it, and deal with it (no rugsweeping or compartmentalizing) it will haunt you for the rest of your life.
Unfortunately, you are now going through what many of us went through (except the walking in on it...which must be a shock like no other), and what some of us have managed to get to the other side of.
This was the most terrible thing I've ever gone through, bar none. No death in my family ever affected me like this. I'd never wish this on anyone, except maybe Hitler.
Rest assured, there is NOTHING that you did that led to this. There is NOTHING that you didn't do that led to this.
THIS HAS NOTHING TO DO WITH YOU AT ALL.
It has everything to do with him and his own internal issues and problems that he is not dealing with in a constructive manner. Your story, terrible as it is, is much the same for us all.
It was unprotected too
It is almost always unprotected sex. People who stop and think to put on condoms don't do this stuff. Having to stop and think makes you think of "why" and "who" and that isn't what your brain is doing when this happens.
"Your are SUCH a baby!"
No, you aren't. You are a young woman, a young mother, and in a vulnerable place in life as well as someone who has been betrayed by the person who was supposed to protect you and your child and who has instead put you both in danger.
"he finds you boring in bed."
That is not an issue at all, much as he may make of it, he may be bored but that is not about you.
If he told her that, then the problem lies right between his ears. If he finds you boring in bed, all he has to do is go to the bathroom and look in the mirror to find out where a huge part of the solution to that problem lies. This has nothing to do with you.
My wife, a perfect example of this type of behavior, as are most if not all WS's, said to me once, rather off handed and clearly without thinking, "you never want to have sex anywhere but the bedroom". This is my wife, who didn't like giving or receiving oral sex, who didn't like vigorous "gymnastic sex" (her words - not mine), who was turning me down when I wanted to have sex practically everywhere, outside in the yard, on the trampoline when we were watching the stars, in the car, when we were camping, in our kitchen, in our living room, in hotels, in the bathroom, in the bathtub, in the shower, and yes, even in the bedroom at home. I looked at her, barely containing my irritation, and said "why would I expect to have sex anywhere else, we don't even have sex there". I'd been turned down for sex in more places, and more times, than I could ever believe.
We'd even been to MC over our relationship. To top it off, she'd had an affair, which I didn't know at the time, and during a short fling, had sex in our bedroom with him, including oral sex both giving and receiving, in our garage, fooled around with him in our yard, been driving him around in our car, been to his house and had sex in his and his wife's bedroom, had sex in the woods, had sex in a local business place with him, had sex with him in a local parking lot, and took him to the park where we had our first date and gave him a blowjob in the park in view of where we parked to get out and take a walk, and she had sex in another person's house and apparently raped by him in their bathroom. Guess who didn't want to have sex? My wife.
Everything triggered her due to a history of sex abuse that she had hidden, that she dealt with by sexual acting out, drinking, and drugs.
It took months of counseling before my wife began to come clean about her drinking and her drug use and nearly 3 years before she dealt with her sexual hangups and stopped blaming me for things that had nothing to do with me. Today, she admits that it was her, from the beginning.
He told me she was 44 and a divorcee and that she had a son.
Don't believe anything he told you yet. She may very well be as noted but she may be married, separated, but she's clearly f'd up and that is clear from what she said to you. She was only trying to make herself feel better about herself. She's more f'd up than you can possibly imagine. She's got nothing on you.
It's not the first time, he told me he slept with her twice at her house while they locked her 6 year old son in the living room
Fairly "normal" routine behavior in infidelity. My wife, who didn't like sex, who was always worried about a kid knocking on the door, did it in our house with 4 kids down the hall watching TV, with a near stranger.
I have no one to talk to
Now you do.
There are a lot of people here who have been through this hell of infidelity. I've seen this happen in my brother's family, and I didn't understand what it was like for his wife as he cheated on her. Now I do, but wish I didn't. I look at my three girls and my son, two of whom are adults now, and hope that they never face this, but know that there is a statistically high chance that at least two of them will.
I didn't find this place until I'd been through two years of a shitstorm that I didn't create. It is helpful. Not all of the advice is good, not all of us are able to give advice at all, but you can get good feedback, understand the sleepless nights, the gut gripping pain, and the mental exhaustion are universal to the BS. That the lies, the trickle truthing, the gaslighting, the blameshifting, by the WS...again, all essentially universal.
Come here, write your story, share your experiences, and read, read everything you can, and don't make any decisions right now but to protect yourself and your child. Also, don't get pregnant again right now, no matter what. He may even suggest it. You don't know yet if he can be a reasonable husband and father to your children. People who do this have serious problems that they are dealing with in a very destructive manner.