I have a feeling that gay3 will do something ridiculous like file a court case for chahat's custody, and heer will think that prem did it. So, she will confront prem, on a rainy night, when he is looking all hot and wet (sorry I just had to throw that in there 😳). She will tell him that she has lost all respect for him and that she can't believe that she loved him or blah blah. Prem will get totally heart-broken and he will decide to marry geet.
Then, on another rainy night, he will confront heer and tell her that he is tired of proving his love for her. He is moving on with his life, for their love's sake and he will give her the WEDDING CARD, and leave.
Soon after, heer will realize that how much she still loves him and how much she doesn't want him to get remarried. And meanwhile, ash's truth will come out. Heer will then go into the i-don't-even-deserve-prem-anymore phase and she'll wish that he does get married and have a good life. BUT, bauji will find out the truth and tell prem and prem will do another wedding tamasha (tahts like his signature move 😃) and he will put sindoor on heer's maang, right there, in front of everybody.