Hello Willowen - I am so sorry to hear about the loss of your music partner. Making music together creates such a strong and intimate bond and I can fully understand why you felt unable to continue without him. But I am equally sure that the kindness of his wife is a message to you that the time has come to move back into the wonderful world of making and sharing music.
I have always felt (and found!) that writing lyrics is significantly more difficult than writing the music. So you are already more than half way there! I have also found that lyrics write the music, rather than the other way round. There is always an emotion and cadence to lyrics to which there can only be one tune. When you write the lyrics, you will hear the music naturally forming in your mind.
Also, music does not have to be complicated. All music does is provide a vehicle for the lyrics, not the other way round. Many good songs are written using just a few notes - as many successful pop bands have found! And the accompaniment can be very simple - just a stroke of a chord on a guitar can be all that is needed. I am not sure if you can play the guitar but if you cannot, just try to learn a very few basic chords - C, F, G, A minor and E minor. Just about every song ever written can be played with these chords. Then sit down in a quiet room with the guitar and the lyrics. If it is a happy song, stroke a C chord. If it is a sad or emotional song, stroke an A minor chord. And then sing the tune that is in your mind. As Gwion said, that tune may turn out to be a traditional one, or a tune you have heard on the radio or CD or your own invention. It doesn't matter. Just sing. The tune may change as you sing each verse and as you sing the song again. It doesn't matter. Eventually, one tune will gel with the lyrics. And now you are ready.
"Make a difference in the world with my voice and music". I heartily applaud and echo this sentiment. It is certainly what I try to do. My personal feelings on this is that if I can touch even just one person with my music, I have made a difference. So, your audience awaits. Singing to friends, to your Grove and in a folk club are both good possibilities. A very elderly lady turned up at my Grove with her guitar on the day we were being filmed for a forthcoming TV series on Sky TV - now she will be singing to the World! And of course you have access to the internet which gives you the potential audience of everyone in the World. If you can, make a recording of a song (it is really quite easy with a basic computer) and post it here - we would all love to hear it. There are also a range of free sites on the web where you can post a song and share it on other web sites like Facebook and Twitter. I do!
So, take a deep breath, feel the Awen and do it. And have fun!