i believe married men can have women friends and that married women can have male friends. that being said, here is my opinion.
these sound like work situations. he has never cheated on you you say so he has never given you any reason to believe that these are any more than casual business relationships. now, if he were going out to lunch alone with these women and it was just as friends and NOT about business, that i would have issue with. i don't think married people, men or women, should put themselves into vulnerable situations. but it is a fine line.
my bf and i had this discussion the other night. someone he dated very briefly but remained good friends with who is significantly younger than him is now engaged. i have known of her since i started getting to know my now bf, and i think in the beginning of us getting to know eachother, she was very jealous of me. (my opinion, he doesn't not agree, that is ok, i am a woman, i know how we think, but we can agree to disagree on things). anyway, i am not 100% comfortable with this girl or their friendship, and i think a lot of it has to do with her age (she just 22 he is 36). she called him and wanted to go out to dinner alone with him to talk about her engagement,etc. i was not at all comfortable with that. he did not go, but we did have a long conversation about my feelings.
it is hard because i believe he can be just friends with her, but i am coming out of a marriage where i was cheated on repeatedly so it is hard for me to say "yes, continue to be friends with and dine alone with this girl you have a history with". but, i have decided, i cannot control who he is friends with and i don't want to.
long story short, bottom line for me is, until he gives me (or in your case you) a reason to believe he is untrustworthy, i will trust him and trust in his decision as to who he feels he can have for friends. and i believe that is what you should do here. what you need to work on is the distance that is in your marriage, marriage problems could turn these working relationships into deeper friendships if he feels he needs to "lean on one of them" because things aren't well in the marriage. never allow that to happen!
are you 2 in counseling or working on the feelings you have for distance?
and if you do talk to him, make sure it doesn't come across as distrust or jealousy. i think men really hate that. both men and women are in business these days and it is unavoidable to have contact with them. i think you two need to take a deep look at your marriage and really come up with how you can always communicate openly. that was a big deal for me in any relationship i may get into after my marriage. and i have to say, me and bf do talk about everything. sometimes it can be heart wrenching, sometimes we cry, sometimes it is just us talking. but we leave NOTHING inside and i really don't think you can. i love that we talk about everything. sometimes it is not always comfortable but we do it.
good luck...
mlhb