Should I get divorced or should I pretend like nothing happened?

I know this will sound crazy,unbelievable and most of you will think it's made up but I'm a middle aged man and I'm too old to make up ridiculous stories.What I'm about to narrate is 100% true and I'm heartbroken.I need more opinions which is the reason why I'm turning to you guys.

Let's cut to the chase.Me(43 years old) and my wife(42) have been married for 17 years.We have a daughter(12).In the beginning our marriage was going great.Eventually,though,me and her became distant.I really don't know why.Maybe it's because I'm always working,I'm not a workaholic but since she's a stay at home mom/housewife I have to work in order to support our family.She only makes sure the house is clean,does the dishes and helps our daughter with her homework.We stopped having sex that often.We were in a rut.However,I still managed to make time for her and she never complained.Recently,she's been acting suspicious.I've been suspecting her of having a secret lover.

It was eating me up so I decided to talk to her about it.She laughed and said:Honey,don't be silly.I only have eyes for you and kissed me.I believed her.I am a businessman,I work for this company and I go out of town on business trips quite frequently.2 days ago,I decided to put her theory to the test so I lied I'd be going on a business trip for the weekend.I got home early and caught her on her knees blowing some young guy very pationately as he was leaning against the dining table.He was fully naked and she was wearing one of my shirts,unbuttoned with an untied tie around her neck.I was so shocked.

She was making comments about how big and yummy his penis was and how she could suck it all day and he was asking her questions such as:"Bigger than your husband's?" and "Do you suck your husband with that much enthusiasm?" To which she replied:"I never do this for my husband,baby!" as she blew him for another 20 mins and then he came in her mouth and a little bit on her hair,it was a lot,some dripped on her boobs and on my shirt(which was expensive),there was also some on the floor.Then he said:"Oh man you're the best baby!"She laughed and said I quote:Shall I clean your cock like the obedient housewife that I am?" To which he didn't say anything so she looked into his eyes with a smirk on her face and put his dick back in her mouth for mere seconds,then put it back out,slide it across her lips and said I quote:"I'll give my husband a nice kiss when he gets home."and started giggling,then she added:"When he ****s me on Monday,I'll be thinking about you."and kept blowing him.I couldn't believe this was real life.I was just standing there so close to them yet they were so caught up in what they were doing they didn't notice my presence.

It's a good thing our daughter was still at school.I couldn't bear to watch any more of that so I went to a pub nearby.I didn't drink,I just stayed there for hours.Later on,she had the nerve to call and ask me how I was doing and of course,she acted as though nothing happened.What should I do?File for divorce?And what about our daughter?She was the perfect wife.She was so conservative.I never thought in my wildest dreams she was capable of this.And it's true what she said.She's never given me head and we have never done anything kinky.It was as though I was on the set of a porno.I can't get over what I saw.I'm on the verge of a mental breakdown.Any advice?