I think my marrage is dead

I have been married to my wife for 15 years. We have been together for 20 years. In the first 7/8 years she was very jealous person and I lost touch with most of my friends. We have 3 kids together now 17/13/11. 14 years ago I found out she was having an affair we haven’t been married a year. But we worked on it. Then one of my friends told me that they had sex after a night out in an alleyway on the way home. About 12 yours ago we thaught we would try swinging and did for a year or so. We only ever had guys join us as she said she didn’t want me to be with another woman. She has had another 3 affair’s since then. Now we don’t have any kind of sex life. I don’t think she is having an affair this time as she is too busy with work and kids. How do I try and get this marrage back on track.