i'm sorry to hear you don't get to see your husband much. that must be difficult and put a lot of pressure on you.
as for the weed, it's all about context, really. i have always viewed it as something social, or something you'd smoke at the end of a day to help yourself unwind. and this shouldn't be a problem. however if you're getting up in the morning and the first thing you do is smoke weed, it can't be very good for you psychologically!
i suppose 'everything in moderation' is the key. you have to ensure you aren't becoming dependent on it. my boyfriend smokes a lot of weed, for example, but he's given it up for lent many times, and if he hasnt the money to afford it, then he doesn't smoke it. there is no element of addiction whatsoever.
just keep your head screwed on, enjoy a bit of a smoke now and again, but don't forget that there are other ways to help yourself relax! things such as swimming, when you have the time, could be therapeutic. have a friend or friends over every few evenings. just don't make weed the be-all-and-end-all, and you should be fine.
i guess what you should be more worried about isn't the weed, but the problems you are having which made you feel you needed it to relax. can you cope raising your son alone 3/4 of the time? maybe you could use some more help from relatives or a nanny. maybe even having more phone contact with your husband could make you feel better or less lonely. just some ideas...