What should I do!?

so a coworker and I have been knowing each other since February 2017. We hardly even talked to each other .Mid May I would give him rides home and we would go out on the weekends as friends. I never actually saw anything interesting on him at all . Till we actually caught feelings for each other in June.. after his 3 year break up with his ex because he caught her cheating on him . We where basically dating but he never made it official . He met all of my family and I met his . We would be together most of the time.One day I drove by to surprise him since we were supposed to go out (which we planned a month in advance) and caught him with walking with his ex towards the parking garage .Yes, they both saw me ..I stopped for a sec and said "so I guess you're not going anymore?" And he said "well I'm gonna go get breakfast " alright cool ,then drove off and cried my eyes out the whole day .

2 days after , we decided to go out for lunch and talk about that day. We basically agreed to take things slow and that she only went by to "talk about things ". After that ,we went two weeks straight without talking . We've been talking more but his ex still calls/texts him ??what should I do?🤷🏻‍♀️