What should I think about this email?

AS you point out it's a professional development and not a personal development.

It sounds like he might value your opinion on something and is interested in hearing it.

It could also be an attempt to get back with you and it's a round about way of doing so.

I would do as you should, not respond and just leave it alone. He does have another person in his life that he should be talking with. I am sure you are not the only other outlet for him to talk to as well. Keeping yourself out of the middle of something is usually a good policy to have.

Unless he is truly showing that it is a professional thing and you have experience with that professional thing, it's not a good idea to entertain it.

I think its beccause he would like you to know that hes doing good. Not that you care, but he likes to think that you do, which is why he emailed you out of nowhere. Id suggest not emailing back since you said he IS in a live in relationship & you wouldnt want to get in the way of anything.

may be like he threw you out of his life the present one must have also kicked him so he needs u now.

the straight truth is he misses banging you and is handing out a "carrot" to see if you would show enough interest to hook up with him.