Saturn and Lillith, and other things.
Saturn in synastry can refer to many things between two people. It can indicate if a relationship will last or not, and how long, since Saturnian energies include the passage of time and how serious something is, or is not. His Saturn being in your 7th house could mean he brings the relationship a sense of meaning; there is a reason for you to be together. Saturn elongates time and makes us aware of what life is made of, and because of that brings with it a deep sense of meaningfulness. This can actually be a good thing if one is looking to get married. His intentions may be something you are very concerned with, and he may be very intentional with why he is with you. That however, can bring an element of detachment, coolness, or intellectualism to his attitude towards your relationship, or a sense of practicality, perhaps to excess, or simply magnified, and the how best the relationship serves his entire life, if it is to serve any long-term purpose at all. Saturn has to do with our fulfillment of plans, obligations, goals, or some combination of the three, and anything involving Saturn is not to be taken lightly. In synastry, it makes sense he would bring to your attention serious, life-long commitments, not just from his saturn being in your seventh house, which has to do with marriage, but your saturn which falls into his fifth house, which has to do with children.
The "harsh lessons" you describe probably have less to do with a singular interpretation of Saturn in the 7th house, but of how his Saturn in your 7th house impacts your entire chart and how your Saturn impacts his entire chart. From what I gather, it is more your Saturn falling in his fifth house, the house which is associated with all things that bring joy, entertainment, love (not commitment but the "butterflies" or simply flirtations), that is making you feel this way. He is bringing a structure or reason to the side of your life which has to do with experiencing pleasure as merely a part of life, and no reason beyond that. Instead he is now forcing you to examine what makes you happy and why, and what was once light-hearted suddenly becomes associated with serious responsibilities. Has he dramatically changed your social life? Do you find you have less time for play now that you are with him? Are you suddenly concerned with how mature, or immature you may seem? Does he make you find yourself questioning and analyzing why you do the things you do, particularly whether its right or wrong, and if it is a "waste of time?"
The other thing to consider is natally for him Neptune squares Venus, so he is probably pretty idealistic in affairs and relationships, and almost any relationship brings out his idealized view of how relationships work. This isn't a bad thing on either end of the matter, and we all do this to some extent. For you it means you'll want to consider if maybe things feel "harsher" because he has high expectations, and may be more critical than he realizes, as Venus in Virgo is discriminatory and Neptune can make things unclear or blurry when squaring the energies of another planet. In other words he may not even know he is making you feel the way you are. Plus the attitude you describe could have to do with his Jupiter in your 7th, with Jupiter making a sesquiquadrate with your Saturn, meaning there may be this element that you feel you have to "earn" the relationship, or one or both of you feel like it is important, and even a struggle, to give the relationship the kind of depth and meaning that you want.
As for Lillith, the mythology around Lillith is important to consider, and has a lot to do with how one analyzes Lillith as a symbolic figure of human consciousness. In other words, what does Lillith represent, if anything in the natal chart? It has a lot to do with an application of the lore around Lillith and what you believe or don't believe. I happen to think of Lillith as that which depicts a deep, unbridled receptive quality in everyone that can result in strong action based on how one receives other people and the balance of power between how much we give and get in relationships, and our attitudes towards them. That said I would say his Lillith falling in your 7th house might mean he really, ardently passionately enjoys your company, but may also require, or ask you to take control or tell him what it is that you want from the relationship and he may be very vocal or find it important to make it clear what he is willing to give.
