I looked up sag man and libra woman compatibility (of course doing a birth chart analysis is more accurate) here are some things id be looking out for if he does come back………
Sagittarius man and Libra woman make a pairing that is successful, inspiring and motivating. A lot of what he seeks is fulfilled by his Libra woman lover and the sooner she assures him of this the better
If she can successfully keep her Sagittarius man within her reach and she shows him the love and adoration he wants in a woman, the bond becomes harmonious and well balanced between them. This is easily attainable as long as she is not married to her career and gives more attention to him. As she goes off on frivolous matters that don’t make much sense or mean a thing to him, she can quickly lose his interest and perhaps her love.
If he is patient enough with her, she is truly his in no time.
Even though he feels the need to roam and satiate his hunger for freedom, she tends to somehow soothe this need into a calm that he feels so comfortable in.
Moreover he also gets bruised by her masculine attitude which surfaces’ time to time giving him lip lashes.
The sag man i knew did this often……….left………..came back……….left…………..came back…………quite a few times until i put a stop to everything. Not sure if yours has done this or not, if so……….id say chances are he might come back, but if he does (and you want to make the relationship work) then id take the above in to consideration. I dont base everything on astrology but i do use it as a nice guideline and it has seemed to do well with me. If he doesnt come back…………. being your a libra woman ( basing this on the libra women i have known) im sure you are a strong person, and i truly believe you can get over this and forget about him. Good luck:)