I am gay and I live in Keller. But my main question to you is, what are you planning on doing that would jeopardize your safety? Are you planning on walking down the street holding hands, showing affection in public, etc? Although I don't think you would have any problem doing that in Keller per say, there are always people around you that would object that behavior and therefore it would be in your best interest to withhold that type of affection to yourself.
If you are asking if you can live in a home together and will you be safe if your neighbors know your sexual orientation, yes you will probably be just fine, again as long as your neighbors are accepting. This is such a tough question, sorry that I am unable to provide a solid answer. At the end of the day, you are moving to Texas, not San Francisco, so just keep that in mind.
If you are at all interested in country dancing, or enjoying the nightlife as a gay couple, your best bet is Cedar Springs Rd. in Dallas. You will feel totally welcome, but it will be a good 40-45 minute drive for you from Keller.
If you end up coming to Keller, welcome - it's a nice town and I'm sure you'll be safe and enjoy your time here. :)