Wife cheat me for no having sex

Hi all

The situation: 17 years of relationship , 3 years marriage , 1 kids of 3 years .

Not having sex for 3 years with wife . From the birth of our child . Why ? I don’t know. Before also sex was not so great . 2-3 times per month . Maybe I have some problem about sex . ..I think pornography and masturbating get me in this situation.Not cheat her never . She have some intents to have it, but always I found some reasons to refuse him .We didn’t talk so much about this. Sincerely our marriage is more like a friend-relation and mostly around our kid . In last years the attraction and live disappeared from my side . Is just routine and habit.

Recently I found some messages in her phone with a guy from his job and I think she cheat me with him .

Now what the hell should I do? I love my child very much and I can't imagine him growing up with another father. A part of me (30%) would accept to forgive her just for the child . But a part of me feels betrayal and angry , and I don’t know I will can forgive what she do. because she cheated on me.

I know that we ended here also because of me, but I would have preferred she to talk to me and divorce in other terms .

She didn’t know yet I saw messages in his phone.

What to do ???Divorce or not ?