If you have been trying to grow a traditional  lilac tree or Syringa then the sad news is that this shrub is a cold winter plant that needs to go dormant in the winter so must be kept  outdoors. Perhaps you meant to say lavender tree not lilac tree? If you did have a tree lilac on your patio and then brought it indoors in the winter to protect if from the cold it should have gone back outdoors as soon as below freezing weather was over. I suggest you take your sad lilac outdoors now, dig a hole and plant it. If it survives the winter it will sprout fresh new growth in the spring and can stay outside all year long. Keep growing, Marianne Binetti