I would imagine that having a betrothed return from a trip visibly pregnant would be crushing. I can only imagine Joseph's heart-sickness over this. What did his friends say to him? Was he ridiculed? What did his parents say to him? How very, very hard. But God is so faithful. He spoke plainly to Joseph and worked mightily in his heart and mind. We don't see Mary working to convince him, she simply trusts. She trusts that the Lord will do exactly what He promised and will work in Joseph in the way and time that will cause him to also trust the almost preposterous news that Mary shared with him. Joseph's story is one that clearly shows how able and how trustworthy the Lord is. Joseph's story reminds us that, more often than not, we need to step aside and trust the Lord's work in the hearts of men. His story also reminds us that when the Lord calls us to something that is so far beyond ourselves, so far beyond what seems reasonable, He will provide. He'll work in hearts in just the right way at just the right time. He is the God who does exactly what He says He will do. He is a God we can trust.
"Joseph, son of David, do not be afraid to take Mary as your wife; for her Child who has been conceived in her is of the Holy Spirit. She will bear a Son; and you shall call His name Jesus, for He will save His people from their sins." Now all this took place to fulfill what was spoken by the Lord through the prophet..." Matthew 1:20-22