Some background....

I'm a married man in my 30s, been with my wife for 15 years. She's had previous partners before me, she's my one and only....

About a year ago, my wife and I came to the conclusion that we both wanted to try threesomes, both MFM and FMF. I'm struggling with the idea, not because of any lack of trust but I'm concerned that if we start down this path, it alters our relationship and marriage. I'm struggling with the idea of, after 15 years, that she won't be my only partner and what if this somehow changes my perspective on sex. Will I still feel the same way when just she and I sleep together or will there be less of an emotional entanglement? How far do we take this? Do threesomes turn to swinging, then to an open marriage? Whilst I'm not shaming the lifestyle, I know it's not for me. My whole rationell is that as long as we're sleeping with other people together, we're not leaving monogamy behind, we're simply allowing, for a very short period of time, someone else to venture in. I very much want to keep an open mind and help us both explore our fantasies but I think my time in a longterm relationship with no other exposure to others, has put me at a disadvantage.

Any advice is welcome.

Thanks.