Let me start by saying that it sounds like you are only going to be able to have one or the other: LS or wife.
That being said, what can you do to try and have the slight chance of joining the two? Same formula as most of us in the LS. Work on the big three: love, trust and communication. Keeping in mind that some (most) people are just not wired for swinging, one of the main reasons is that when the subject is broached, the partner instantly thinks 'why aren't I enough for them' or 'why are they looking for a replacement for me'. This is because there has been an erosion of love, trust, communication or a combination of all three. The place to start is to improve your communication. You need to show your partner that they can tell you ANYTHING and you won't pass judgement or run away screaming because what they said is so shocking. As the communication improves, so does the trust. As the trust improves, so does the love. Our tag line at the bottom really says it all: If you don't have to lie about sex... This is not going to happen over night, but you do have time (the rest of your life) and the WORST thing that can happen is your relationship improves (no matter how good it may or may not already be). So work on that first. Then start talking about your sexual fantasies. Do this outside of a romantic event and start slow (don't just start off with 'I want to sleep with other people' again). Find the ones you both have in common and act them out. Among other things, your wife needs to relearn to be a sexual being again. She has been a 'mom' for a long time and needs to be reminded that she is also a woman. This is something that she probably needs anyway. Start with this and see what happens. She may not ever be interested in the LS, but if you want to take a shot and try, this is the first step, and will only make your relationship better even if she isn't interested.