It's a kind and caring gesture, but holding an umbrella for both of you while it's raining doesn't necessarily indicate love on its own. Love is a complex emotion that involves a deep affection, connection, and mutual understanding between two people.
The act of sharing an umbrella during the rain can certainly be a sign of consideration, thoughtfulness, or even a friendly gesture. It may also indicate that she cares about your comfort and well-being. However, to determine if it's love, you need to look at the broader context of your relationship and the emotions and behaviors you both share.
Love involves a range of feelings and actions, including trust, respect, emotional intimacy, and a willingness to support and be there for each other in good times and bad. If your relationship has developed into something more meaningful and significant, where you both care deeply for each other and demonstrate love in various ways, then sharing an umbrella can be one of many small expressions of that love. But remember, it's not solely defined by this one action alone.