I've seen (& sometimes heard) this topic discussed dozens of times, and got the impression > 90% of blokes would hate it if this happens, even if they themselves are punters.
Personally I'd not be that bothered, which may be due to 3 reasons 1) I don't really see sex work as immoral. 2) Beggars can't be chosers, & I'll take any half decent sexual relationship I can get. 3) I might have something of the 'cuck' about me (to be fair it might be just I pretty much never feel jealous about anything, the thought of watching some other bloke banging my bird doesn't turn me on at all, & I've never even been to a swinger party)