Child support help in PA?

My wife left me stuck with a 1300. mortgage only in my name, which I can't sell because right now it's basically worth about 2k less than what I owe on it plus realtor fees means it would prob cost me at least 6k just to sell it. The divorce has not been filed yet she left me about 6 months ago (cheating for the second time) and we agreed on 500 a month support for our (2 kids pre school age) because that's what it looked like I could afford without loosing the house but now she is threatening to take me to court if I don't pay her 800 a month. I have the kids Tues and Wed from 8-2 because I work second shift and then Fri 8am till Mon morning 8am with her picking them up every other Sun night at 7pm so I could get a night out every other week even though it's Sun. She is also telling me that even though I spend a lot of time with my kids being that it's not over nights they don't consider it and she could prob get even more if it went to court based on the support calculators. I just want to know what to do I know I need to see a lawyer but are the things she’s been saying true?