While one-night stands are not exactly the most healthy way to deal with heartbreak, maybe you should have taken her for her offer. You need to broaden your horizons and move on. Also, she seemed pretty into tickling, too...
Guy has two girls willing to let him tickle them throwing themselves at him, and he still wants the woman who's willing to cheat on her fiance with a high school boy.
This MC gets dumber and dumber every chapter. Instead of going for the girl who is genuinely into him and lets him do whatever he wants or the new girl who is also into it and can probably help relieve him of his tickle desires. He instead chooses the woman who is getting married and molests her.
He's a really serious kid, he thinks having sex equals going out, or something even more serious. Hence he says he can't do that, cuz he can't take responsibility for that action and go out with her.