Break up with EX, what to do?

this is a weird and confusing situation... my ex and i broke up back in march, she "needed time and space" 3 weeks later she came back saying how sorry she was and whatever. i was devastated at the time, but eventually got over it and then bang.. she just pops back up into my life. i forgave her and decided to work on things. she left for 3 months this past summer and we spoke but didn't see each other which really hurt our progress on things. i left for school and things never really took off. i found out she started talking to some guy at home and addressed it and she said they have hung out, they do speak, and they're friends. I've always had a suspicion about that because it was always weird. in october i actually caught them hanging out when she said she was somewhere else. i brought it up and we got into a fight. she said they're only friends blah blah blah. after that i was fed up and just cut contact all together. 2 weeks later (this was in november) she texted me saying she wants to work on things and be together and the whole 9 and what not. i agreed to start talking again but wanted to know everything that has happened in the past so there were no surprises. things went okay, but it never seemed like she was giving the full effort i was to make things work. we go to the same gym and she would barely speak to me there, but we would see each other and do errands and go for dinner about 2-3 times a week. well.. about a week ago she was at the gym and was talking to this guy (the one that i caught her hanging out with when she lied months prior) and was ****. i texted her asking if she's sure its not anything more than a "friendship." well that caused a huge fight about me "not trusting her" and how "we continuously take steps backwards". i, once again, apologized and said it was my fault. she hasn't spoken to me all week and I've reached out a few times but have given her space. THEN, two days ago and yesterday she is talking to and hangout with the SAME guy at the gym. coming with each other, leaving with each other. i haven't said anything and neither has she. i am literally so confused and have no idea what to do if anything. as of right now i consider things to be completely over.. any brutally honest insight would help, thanks