I've put in bold how it's been for us. We do this with the same guy. We started out slow and worked up to getting comfy with this.
We are pretty conservative, wife especially so. It's not cuckold for us, we both have sex with her, always all three of us together, they never get together without me.
Wife won't really talk about it with me, she says sex with him is different not better.
WHILE he's with us it's VERY obvious she likes the sex they have. She's constantly saying how good it feels when he's doing her. She moans a LOT with her eyes closed. We take turns doing her and it's a way different view watching but the way she moves with him tells me she loves it.
I get jealous feelings seeing how turned on she gets with him but it's all good.
We don't use rubbers when he's with us, we both usually cum inside her. We don't play with the sperm, she wipes off between rounds(usually) but the mess is part of the sexy fun.
After he's been with us she's horny as fuck for days after so we have a lot of very good sex.
We aren't swingers, none of our friends know we do anything like this.
Our fun with him has improved our sex life like crazy.