People relocate all of the time for family or loved ones. If the subject comes up, simply state that you are relocating for personal reasons. Your potential employer has no need to know those personal reasons. If pressed, then you can either say you have family/good friends in the area (IMO, moving for an SO makes that person family ) or state that you are not comfortable discussing it.
If you can send a cover letter (even if it is not required, but is an option) then do that. If not, then I think changing your Objective to state you are relocating would be a good idea. When I get a resume then I assume that the person is willing to relocate, but then I live in a rather large metropolitan area. If I was in a small town, I am not sure how I would react because I have not BTDT.
Do not tell your boss that you are looking. Take a vacation day if you have an interview. If she asks, then tell her you are visiting SO (I assume that you would visit SO if you are in town for an interview...) Companies will generally work with you on scheduling interviews because they know you are working while you try to find employment. So you will probably be able to schedule most of the interviews on a Friday or Monday, making a long weekend visit with your SO.
Finally, research each company before you submit your resume and try to target your resume and cover letter to their specific need. That is, what is in a company in a smaller town may not be exactly what you currently do. For example, if you have experience in accounting in a large corporation, try to explain how that will benefit a smaller locally owned company.